Francisella tularensis is one of the most infectious pathogens known to man, as few as 10 organisms can cause disease. Aerosolized F. tularensis represents a potentially dangerous biological weapon. Alveolar macrophages (AM) constitute both the principal target for intracellular replication and a key effector for the elimination of F. tularensis deposited in the lungs. Infiltrating neutrophils are a prominent feature of pneumonic tularemia. Factors judged important in host defenses to F. tularensis are based largely upon studies involving mice inoculated intravenously. The role of specific defense mechanisms varies, however, dependent upon the route of infection (i.e., inhalation vs. systemic) and primary site of invasion (lung vs. spleen or liver). Recent studies conducted in our laboratory indicate that the interaction between inflammatory neutrophils and resident tissue macrophages plays a critical role in host defenses to bacterial infections expressed in the liver. Similarly, it is speculated here that neutrophiI-AM interaction exerts a significant influence on innate resistance to F. tularensis in the lungs. The SPECIFIC AIMS of this proposal are to: I. Delineate the biological response of AM to aerosolized F. tularensis, i.e., IA. quantify phagocytosis of F. tularensis, apoptosis and the antimicrobial activity of AM, lB. quantify cytokine and chemokine production, IC. assess the intermediary role of AM in the infiltration and bactericidal activity of neutrophils, and ID. define the role of AM in down-regulating neutrophils sequestration and tissue injury. Il. Determine the effect of infiltrating neutrophils on proinflammatory cytokine and chemokine production by AM. Given the limited number of relevant studies to date, the results of the proposed experiments should dramatically increase our current understanding of the factors that effect innate host defenses to pulmonary F. tularensis infections. This, in turn, should enable the development of innovative strategies to improve treatment and prevent the fatal consequences that often occur in untreated cases of pneumonic tularemia. Moreover, our primary approach to studying cytokine gene expression by inflammatory cells (i.e., immuno-laser capture microdissection followed by GeneChip expression microarray analysis of mRNA) should afford considerable insight into the factors, pathways and underlying mechanisms that effect innate immunity to respiratory infections in general.